Boundary wall structures for hot fluid streams



9, 968 L. F. RICHARDSON 3,362,470

FOR HOT FLUID STREAMS BOUNDARY WALL STRUCTURE 2 Sheets-Sheet 1 Filed Oct. 18, 1965 4. I'll.

I'll- Jan. 9, 1968 L. F. RlcHAnbsw 3,362,470

BOUNDARY WALL STRUCTURES FOR HOT FLUID STREAMS Filed Oct. 18; 1965 2 Sheets-Sheet 2 United States Patent 3,362,470 BOUNDARY WALL STRUCTURES FOR HOT FLUID STREAMS Leslie Frederick Richardson, Bristol, England, assignor to Bristol Siddeley Engines Limited, a British company Filed Oct. 18, 1965, Ser. No. 497,360 Claims priority, application Great Britain, Oct. 20, 1964, 42,717/ 64 4 Claims. (Cl. 165134) ABSTRACT OF THE DISCLOSURE The disclosure of this invention pertains to cooling a wall by forming a film separating a wall to which a cold fluid passes from a wall through which a hot fluid passes in a gas turbine jet engine.

This invention relates to boundary wall structures for hot fluid streams.

It is known to cool a wall dividing a hot fluid flow from a cold fluid flow of higher pressure by providing at the wall a passage admitting some of the cold fluid for the latter to form a film separating the wall from the hot fluid.

It has been found that for good cooling efficiency the velocity of the film must be related to the nature of the hot flow. Also the film should be free from undue turbulence. It can be the case that the pressure difference between the hot and the cold flow is too high for the establishment of a satisfactory film. The main object of this invention is to overcome or reduce this difiiculty.

According to this invention a passage system for cooling a wall dividing a hot fluid flow from a cooler fluid flow of higher pressure comprises:

(a) A chamber formed at said wall;

(b) An inlet opening connecting the cold flow side of the wall to the chamber;

(c) An outlet opening connecting the chamber to the hot flow side of the wall;

(d) The interior of the chamber defining a flow passage extending between said openings and shaped to direct flow from the high pressure side of the wall through the outlet opening so as to form a film between the wall and the hot flow adjacent thereto;

(e) The flow passage including a substantially sudden enlargement of the flow area to create turbulence in the flow and thereby to reduce the mean velocity of the flow without a significant rise in static pressure;

(f) The flow passage including, downstream of said sudden enlargement, a portion of substantially uniform flow area to assist in settling said turbulence and in forming a uniform flow; and

(g) the outlet opening being dimensioned for the effective flow area thereof to be not less than the effective flow area of the inlet opening.

A constructional example of this invention will now be described with reference to the accompanying drawings wherein:

FIG. 1 relates to the first example and is an elevation of a gas turbine jet engine shown partly in section and including a combustion chamber.

FIG. 2 is an enlarged detail of the said combustion chamber.

FIG. 3 is a section on the line III-III in FIG. 2.

FIG. 4 is a section on the line IV-IV in FIG. 2.

FIG. 5 is a section on the line V-V in FIG. 2.

Referring to the drawings, the engine (FIG. 1) comprises a compressor supplying air under pressure to the interior of an air casing 11 which surrounds a series of can-type combustion chambers 12 of which only one is shown. Fuel supplied to the chamber 12 through a supply pipe 13 reacts with air entering the chamber 12 through holes 14 to produce a flow of burning gases which is exhausted through a turbine 15 which drives the com pressor 10. The temperature and pressure conditions at the wall, denoted 16, of the combustion chamber 12 are such that at the outside of the wall 16 there exists a flow 17 of air which is substantially cooler and has a substantially higher static pressure than the flow 18 (FIG. 3) of the burning gases at the inside of the wall 16. Some of the air at the outside of the wall 16 is allowed to enter the chamber 12 through a passage system 20 in such a way that a layer or film 19 of this relatively cool air is formed at the inside of the wall 16 to protect it from the heat of combustion. The film is only effective for a limited distance downstream of the passage system 20 because it tends to dissipate. Therefore it is usually necessary to provide two or more passage systems 20 so that the film 19 is renewed at intervals along the length of the chamber 12. The efficiency of the cooling can be measured in terms of the distance, downstream of any one passage system 20, over which the film is effective in preventing a rise of the wall temperature above a predetermined value.

It has been found that for good cooling efficiency the film 19 should have a uniform flow, i.e., it should be free from undue turbulence and there should be no undue velocity gradients in the cross section of the flow. Further, it has been found that cooling efficiency can be improved by adjusting the velocity of the film in relation to the velocity of the combustion gases, and as a general rule the velocity of the film should be approximately the same as that of the mean velocity of the directly adjacent part of the flow of the combustion gases so that mixing between the two flows 18, 19 is minimized. The term means velocity is applied to the combustion gases because of the turbulence of these gases. FIG. 2 shows purely diagrammatically a desired velocity profile 21 for the film 19, an indication at 22 of the velocity profile of the hot flow 18, and at 23 the junction of the flows 18, 19 across which mixing should be minimized. It is one of the objects of this invention to provide means for bringing about these desirable conditions. In this connection one must have regard to the pressure drop across the wall 16, i.e., the pressure difference between the flows 17, 18. This pressure drop has to be high enough to force combustion air through the holes 14 in such a way that the air penetrates deeply into the chamber 12. It has been found that such a drop is usually too high for establishing a cooling film of good uniformity of flow and of a velocity sufficiently low to match the velocity of the adjacent hot flow. The difliculty is overcome or reduced by the construction described next below.

The passage system 20 comprises a chamber 24 (FIGS. 2, 3) situated at the wall 16 and having an inlet opening 25 from the cold flow 17 and an outlet opening 26 to the interior of the wall 16. The chamber 24 is constituted by an outer wall 27 which is a portion of the wall 12, and by an inner wall 28 which has a curved portion 29 closing the upstream end of the chamber 24. Between its inlet and outlet openings 25, 26 the interior of the chamber 24 defines a passage 30 and air flow is established through the passage 30 on account of the pressure drop across the wall 16.

The inlet opening 25 comprises holes 31 in the wall 16. At the outlet opening 26 a corrugated strip 32 is secured to the wall 27 in position between the walls 27, 28 partly in order to ensure that the Walls 27, 28 remain at their correct spacing, and the outlet opening 26 is defined by spaces 33 between the corrugations of the strip 32 and the walls 27, 28. The holes 31 and spaces 33 are so dimensioned that the effective flow area of the spaces 33 is not less than the effective flow area of the holes 31. As a result it is the holes 31 which meter the flow through the passage 30 and the static pressure drop across the passage 30 occurs substantially at the holes 31. Immediately downstream of the holes 31 the passage has a sudden enlargement 34 of the flow area which has the effect of creating turbulence and thereby reducing the mean velocity of the flow without a rise in static pressure. Downstream of the enlargement 34 the passage 30 has a portion 35 of substantially uniform flow area whereby the turbulence created at the enlargement 34 has the opportunity to settle and the flow approaches the outlet opening 26 in substantially uniform manner. The corrugations of the strip 32 assist in making the flow uniform for two reasons. Firstly, since the flow area of the spaces 33 is necessarily less than the flow area in the portion 35 there is created in the portion 35 slightly higher pressure than would otherwise be the case, and this helps in the settling of said turbulence. Secondly, the sides of the corrugations help to straighten the flow because they lie parallel to the intended direction of flow.

In many cases, because of the random nature of the hot flow, it is difficult to determine the mean velocity of that part of the hot flow which influences the cooling film and the optimum film velocity is obtained experimentally by adjusting the outlet opening 26. If the distance between the walls 27, 28 is reduced at the position of the strip 32 then the velocity of the film increases and vice versa. However, the flow area of the outlet opening must not be so reduced that it becomes less than the flow area of the inlet opening because then the film velocity would rise to a value exceeding that of the inlet velocity.

The wall 28 is secured to the wall 27 by rivets 36 situated downstream of the inlet opening 25 so as to be cooled by the air flow. The flow through the passage 30 is also important for the cooling of the wall 28, and the curved end 29 of the wall 28 is situated close to the holes 31 as otherwise it would not be able to benefit from the cooling effect of the incoming air.

What I claim is:

1. A passage system for cooling a wall dividing a hot fluid flow from a cooler fluid flow of higher pressure comprising:

(a) a chamber formed at said wall;

(b) an inlet opening connecting the cold flow side of the wall to the chamber;

() an outlet opening connecting the chamber to the hot flow .side of the wall;

(d) the interior of the chamber defining a flow passage extending between said openings and shaped to direct flow from the high pressure side of the wall through the outlet opening so as to form a film between the wall and the hot flow adjacent thereto;

(e) the flow passage including a substantially sudden enlargement of the flow area to create turbulence in the flow and thereby to reduce the mean velocity of the flow without a significant rise in static pressure;

(f) the flow passage including, downstream of said sudden enlargement, a portion of substantially uniform flow area to assist in settling said turbulence and in forming a uniform flow; and

(g) the outlet opening being dimensioned to be not less than the effective flow area of the inlet opening.

2. A passage system according to claim 1, including members situated in said passage downstream of said sudden enlargement and having surfaces lying parallel to the intended direction of flow to assist in straightening the flow and settling said turbulence.

3. A passage system for cooling a wall dividing a hot fluid flow from a cooler fluid flow of higher pressure comprising:

(a) a chamber formed at said wall;

(b) an inlet opening connecting the cold flow side of the wall of the chamber;

(c) an outlet opening connecting the chamber to the hot flow side of the wall;

(d) the interior of the chamber defining a flow passage extending between said openings and shaped to direct flow from the high pressure side of the wall through the outlet opening so as to form a film between the wall and the hot flow adjacent thereto;

(e) the flow passage being dimensioned to include a substantially sudden change from the flow area determined by the inlet opening to a larger flow area downstream thereof to create turbulence in the flow and thereby reduce the mean velocity of the flow without a significant rise in static pressure;

(f) the flow passage including, downstream of said sudden enlargement, a portion of substantially uniform flow area to assist in settling said turbulence and in forming a uniform flow; and

(g) the outlet opening being dimensioned to be not less than the effective flow area of the inlet opening.

4. A passage .system according to claim 3, said wall lying substantially parallel to the general direction of the hot and cold flows, the inlet opening being constituted by holes in the wall, and said chamber projecting from the wall into the hot stream.

References Cited UNITED STATES PATENTS 2,658,337 11/1953 Clarke et al -39.65 2,770,097 11/1956 Walker 60-265 X 2,775,094 12/1956 Buckland et al 6039.65 2,785,878 3/1957 Conrad 134 X 2,884,759 5/1959 Sevcik 6039.65 2,916,878 12/1959 Wirt 60-3965 ROBERT A. OLEARY, Primary Examiner.

M. A. ANTONAKAS, Assistant Examiner. 

